I was sifting through some of the employees character profiles (they have early access) and came across a few interesting tidbits of info that might be evidence of gun customization. First, there was a new vendor in the Tower Allies section of the grimmoire. It was a tower droid classified as Frames, most likely referring to the product they sell. I'm guessing this vendor sells weapon frames. I came across a few weapons in people's inventories that had prefixes on their names. Painted and Silvered were two in particular. When I viewed them they did appear to have a visual difference compared to weapons of similar color schemes (the silvered one was a crucible weapon, and instead of being entirely red and black, quite a bit of it was silver, like actually shiny reflective silver). This is still just speculation, so don't get your hopes up, but this is still some solid evidence that there might be weapon customization in my opinion. Edit: I have provided a link to the grimmoire of the user Nine-Box. Their Tower Allies section has the Frames card in it.